A diver propulsion vehicle (DPV, also known as an underwater propulsion vehicle or underwater scooter) is an item of diving equipment used by scuba and rebreather divers to increase range underwater. Range is restricted by the amount of breathing gas that can be carried, the rate at which that breathing gas is consumed under exertion, and the time limits imposed by the dive tables to avoid decompression sickness. DPVs can have military application.

A DPV usually consists of a pressure resistant watertight casing containing a battery-powered electric motor, which drives a propeller. The design must ensure that the propeller cannot harm the diver, diving equipment or marine life, the vehicle cannot be accidentally started or run away from the diver, and it remains neutrally buoyant while in use underwater.

DPVs are useful for extending the range of a diver that is otherwise restricted by the amount of breathing gas that can be carried, the rate at which that breathing gas is consumed under exertion, diver fatigue, and the time limits imposed by the dive tables to avoid decompression sickness.[1] Typical uses include cave diving and technical diving where the vehicles help move bulky equipment and make better use of the limited underwater time imposed by the decompression requirements of deep diving.[2]

Military applications include delivery of combat divers and their equipment over distances or at speeds that would be otherwise impracticable.

For many recreational divers DPVs are not useful. Buoyancy control is vital for diver safety: The DPV has the potential to make buoyancy control difficult and cause barotrauma if the diver ascends or descends under power.[3] Visibility of less than 5 metres makes navigating a DPV difficult. Also, many forms of smaller marine life are very well camouflaged or hide well and are only seen by divers who move very slowly and are very vigilant.

The most common type of DPV tows the diver who holds onto handles on the stern or bow. Tow-behind scooters are most efficient by placing the diver parallel to and above the propeller wash. The diver wears a harness that includes a crotch-strap with a D-ring on the front of the strap. The scooter is rigged with a tow leash that clips to the scooter with releasable metal snap.

These are torpedo or fish-shaped vehicles for one or more divers typically sitting astride them or in hollows inside. The well known human torpedo or chariot was used by commando frogmen in World War II. Similar vehicles have been made for work divers or sport divers but better streamlined as these do not have warheads; the Dolphin made on the Isle of Wight (UK) in the 1970s is an example. Some Farallon and Aquazepp scooters are torpedo-shaped with handles near the bow and a raised seat at the rear to support the diver's crotch against the slipstream. The Russian Protei-5 and Proton carry the diver attached to the top. The New Zealand made Proteus is strapped onto the diver's cylinder.

The Subskimmer is a submersible rigid-hulled inflatable boat (RIB). On the surface it is powered by a petrol engine, when submerged the petrol engine is sealed and it runs on battery-electric thrusters mounted on a steerable cross-arm. It can self inflate and deflate, transformimg itself from a fast, light, surface boat to a submerged DPV. Started in the 1970s by Submarine Products Ltd. of Hexham, Northumberland, England, Subskimmer is now a tradename owned by Marine Specialised Technology.

As DPVs get bigger they gradually merge into submarines. A wet sub is a small submarine where the pilot's seat is flooded and the diver must wear diving gear. Covert military operations use swimmer delivery vehicles (SDVs) to deliver and retrieve operators into harbors and near-shore undetected. An example is the Multi-Role Combatant Craft (MRCC).[4]

These are unpowered boards (usually rectangular) towed by a surface boat with two ropes. The diver holds onto it and keeps it submerged by adjusting the angle like an upside-down aerofoil. It is named after the manta ray fish.

All confirmed DPVs in Chinese service are developed by the Kunming Wuwei Science & Technology Trade Co., Ltd[5] at Kunming, a solely owned subsidiary of Kunming 705th (Research) Institute Science & Technology Development Co. (昆明七零五所科技发展总公司)][6] at Kunming, which in turn, is a company wholly owned by the 705th Research Institute (headquartered in Xi'an) of the China Shipbuilding Industry Corporation. All DPV/SDVs (swimmer transportation devices) fielded by this contractor are developed by the design team with the following members: Liu Ning (刘宁), You Yun (犹云), Jin Zhongxian (金仲贤), Chen Haizhen (陈海珍), and Zhang Chun (张春).[citation needed] A total of 4 DPVs have been identified in Chinese naval service:[verification needed]

In addition to the DPVs currently in the Chinese naval inventory, Glory International Group Ltd[11] in Beijing is also marketing two of its DPVs, (GL602[12] and GL603[13]), to the Chinese military.[verification needed]

Sirena DPV is a Soviet human torpedo around 8 m long with 53 cm diameter so that it can be launched from torpedo tubes. Sirena DPV can transport two divers with a maximum range of 11 nmi at speed of 2-4 kn, with maximum depth of 40 m.[15]

Project 907 Triton 1 is a 1.6 t Soviet DPV manned by 2 crew riding astride spindle-shaped vehicle. The vehicle can rest on the sea bed for up to 10 days before being restarted again thus allowing great operational flexibility. Length is 5 m, beam and draft are both 1.4 m, and maximum depth is 40 m. The vehicle has a maximum range of 35 nmi with 6 hr endurance, and maximum speed is 6 kn.[17]

Project 908 Triton 2 is a 5.3 t Soviet DPV manned capable of carrying 6 crew. Although a wet sub, the design incorporates a system to maintain a constant pressure within the submarine regardless of depth. Length is 9.5 m, beam is 2.0 m and draft is 2.2 m, and maximum depth is 40 m. The vehicle has a maximum range of 60 nmi with 12 hr endurance, and maximum speed is 6 kn.[17]

2 men crew SDV with 30+ kn on surface and can be parked on the sea floor. There are three different modules for the Carrier providing different applications including: SEAL SDV – Swimmer Delivery Vehicle for SOP missions, SEAL AUV – Autonomous Under- water Vehicle for MCM missions, and SEAL RWSV – Remote Weapon Station Vehicle for Fire Support.[21]

Smart SEAL

A downsized SEAL Carrier, with 30+ kn on surface and can be parked on the sea floor.[22]

After purchasing US submersible manufacturer Seahorse Marine, Emirate Marine Technologies of United Arab Emirates has developed four classes DPV/SDV, all of them built of glass reinforced plastic and carbon composite materials:

Class 4

Three-ton two-man DPV using silver-zinc external battery packs to power an 8 kW motor. Sensor and control suites include a sonar, echo sounder, GPS, electronic compass and electronic mapping facility and an onboard computer. They have a range of 60 nmi (110 km) at 6 (maximum speed 7) kn and can operate down to 50 m. Maximum payload is 200 kg.[26]

Class 5

Eight-ton two-man DPV using nickel-cadmium external battery packs to power an 8 kW motor. All other specs are identical to Class 4 except the maximum payload is increased to 450 kg.[26]

Class 6

DPV/SDV currently under development to carry 4 or 8 (2 crew) divers. Will have 2 8 kW motors for underwater use and a diesel for surface operations. There will be computer-controlled system--including an automatic pilot to reduce operator workload, and a telescopic mast with a television camera and/or a thermal imager. Class 6 will have a range of 100 nmi (185 km) at 4 knots down to 50 m, but on the surface the diesel will give it a maximum speed of 20 kn. There will be built-in breathing sets for divers to conserve their underwater breathing apparatuses.[26]

Class 8

11 m long DPV/SDV propelled by two eight-kW motors and powered by a lithium-ion battery for 6 divers (2 crew) currently under development. Maximum range is 50 nmi (93 km) at 5 kn with a maximum speed of 6 kn.[26]

1.63 t two-man DPV/SDV developed by Columbia Research Corporation built of fiber-glass. Maximum range is 27.5 nmi @ 5 kn but burst speed of 8 kn can be achieved with its powerful brush-less DC motor and silver-zinc batteries. Maximum depth is 70 m, although it will usually be kept around 45 m.[27]

2.75 t 6 to 8-man DPV/SDV developed by Columbia Research Corporation built of fiber-glass. Maximum range is 56.5 nmi (104.5 km) @ 5 kn but burst speed of 8 kn can be achieved with its powerful brush-less DC motor and silver-zinc batteries. Maximum depth is 91 m, although it will usually be kept around 45 m.[27] Electronics include color liquid crystal displays and color digital charts, while the computer-based navigation system includes GPS and Doppler velocity log. There is also a multi-beam obstacle-avoidance sonar to distinguish targets while the integrated communications suite includes an underwater telephone and a VHF radio.[26]

Developed by Anteon Corp, a wholly owned subsidiary of General Dynamics since 2006, the 107 kg Sea Shadow is for one or two crew and powered by lead-acid batteries. The hull is of molded high-density polyethylene plastic to provide a low magnetic signature while folding bow planes and rotating motors allow the vehicle to be deployed through a 76-cm escape hatch. The Sea Shadow features electronic speed control with a manual back-up mode and an option of electronic drift compensation. Speed, depth, battery duration and voltage details is shown on a liquid crystal display, while there are visual warning signals on low battery power as well as unsafe rates of both ascent and descent. Sea Shadow has a range of 5 nmi (9.25 km) at 2 to 3 kn and at a maximum of depth of 30 m.[26]

150 kg one-man torpedo like SDV with the operator straddling the aluminium alloy hull behind the first of two buoyancy tanks, and the operator can deliver 40 kg of limpet mines of either the 7 or 15 kg size. This SDV has a dimension of 3.72 meter (length) x 0.52 m (diameter) and can be housed in a submarine torpedo tube. The silver-zinc batteries operating a one-kW motor with a range of 8 kn (15 km) at 2.5 kn (maximum speed 3 kn) at a maximum depth of 60 m.[26]

1.41 t two-man SDV with crew ride astride spindle-shaped vehicle. The 4.5 kW DC electric motor is powered by either lead-acid or silver-zinc batteries, providing a maximum range of 23 nmi or 46 nmi. The cruise and maximum speed are 2.8 and 6.5 kn. Navigation equipment comprises an aircraft-type gyro compass, a magnetic compass, depth gauge with a 0 to 100-metre scale, echo-sounder, sonar, two searchlights and so on, all of which equipment is in a waterproof container. The R-2 can operate down to 60 meters with a maximum depth of 100m and a maximum limpet mine load of 250 kg.[26]